Drilling of subterranean boreholes is often performed by rotating a drill bit which is located at a distal end of a drilling string. The drill bit may be rotated by rotating the entire drill string from a surface location and/or by using a rotary drilling motor which is connected with the drilling string and which is located adjacent to the drill bit.
The drilling string may be made up of individual joints of drilling pipe which are connected together to form the drilling string. Alternatively, the drilling string may be made up of a continuous length of coiled tubing which is stored on a large spool.
When the drilling string is made up of individual joints of drilling pipe, the entire drill string may be rotated with relative ease using a rotary table or a top drive on the drilling rig. When the drilling string is made up of a continuous length of coiled tubing, it is relatively more difficult to rotate the entire drill string because the spool must also be rotated.
Drilling while rotating the drill bit only by rotating the entire drilling string is often referred to as “rotary drilling”. Drilling while rotating the drill bit only with a rotary drilling motor is often referred to as “sliding drilling”. Drilling while rotating the drill bit both by rotating the entire drilling string and with a rotary drilling motor is often referred to as “performance drilling”.
Directional drilling involves “steering” the drill bit so that the drill bit drills along a desired path. Directional drilling therefore requires a mechanism for orienting the drill bit so that it drills along the desired path. The orientation of the drill bit during directional drilling is often referred to as a “toolface orientation”.
Directional drilling may be performed using a bend in the drilling string or using a steering tool which is associated with the drilling string.
If directional drilling is performed using a bend in the drilling string, the orientation of the bend must be controlled in order to provide a desired toolface orientation. As a result, steering with a bend in the drilling string may typically only be achieved during sliding drilling, since rotary drilling will result in a constant rotation of the bend and constant variation of the toolface orientation.
If directional drilling is performed using a steering tool, a desired toolface orientation may be achieved either by controlling the actuation of the steering tool or by maintaining the steering device at a fixed actuation and controlling the orientation of the steering tool in a similar manner as performing directional drilling with a bend in the drilling string.
Once selected, the toolface orientation may change in an undesired manner during drilling due to forces applied to the drill bit and the drilling string. These forces may be forces applied to the drill string from the surface location or may be reactive forces exerted on the drill bit and/or the drilling string by the borehole. As a result, it is often desirable to adjust the toolface orientation during directional drilling from time to time to account for such forces and for resulting undesired changes to the toolface orientation.
Reactive torque results from a reaction of the borehole to rotation of the drill bit against the distal end of the borehole. Reactive torque tends to rotate the drill bit in a direction opposite to that which is imposed upon the drill bit by rotation of the drill string and/or by a rotary drilling motor. Reactive torque may cause changes in the toolface orientation and also imposes potentially damaging stresses on the drilling string.
Efforts have been made to provide a drilling apparatus which controls the effects of reactive torque while facilitating directional drilling.
U.S. Pat. No. 5,485,889 (Gray) describes a drilling system and method for use with coiled tubing. The drilling system includes a control device. The control device includes a downstream section which is connected to a drilling tool having a bend axis, an upstream section which is connected to coiled tubing, and a swivel coupling assembly which connects the downstream section and the upstream section. A pump and a circuit are associated with the downstream section, the upstream section and the swivel coupling assembly so that relative rotation between the downstream section and the upstream section causes the pump to pump fluid through the circuit. A flow restricting orifice and a valve are provided in the circuit. The control device may be actuated to form a straight section of a borehole and a curved section of the borehole. In order to form the straight section of the borehole, the control device is actuated to permit relative rotation of the downstream section and the upstream section at a rate which is less than the rate of rotation of the drill bit. In order to form the curved section of the borehole, the control device is actuated to prevent relative rotation of the downstream section and the upstream section, thereby facilitating orientation of the bend axis of the drilling tool. Actuation of the control device to prevent relative rotation of the downstream section and the upstream section is achieved by actuating the valve to a closed position so that circulation of fluid through the circuit is prevented. The valve is actuated from the surface location through a control cable which extends to the surface location. A sensor communicates through the control cable with the surface location in order to communicate unspecified information to the surface location.
U.S. Pat. No. 6,059,050 (Gray) describes an apparatus for controlling relative rotation of a drilling tool due to reactive torque. The apparatus includes a first member and a second member which are relatively rotatable and a hydraulic pump having a first pump part mounted on the first member and a second pump part mounted on the second member. The pump is arranged such that relative rotation of the first and second members causes relative rotation of the first and second pump parts, which results in pumping of hydraulic fluid from a first chamber to a second chamber within which the hydraulic fluid is under pressure. A brake having a first brake part on the first member and a second brake part on the second member is associated with the second chamber such that the brake is actuated by the hydraulic pressure in the second chamber. A duct and a variable orifice control the flow of fluid from the second chamber back to the first chamber, thereby controlling the braking force exerted by the brake and the relative rotation of the first and second members. The apparatus may be actuated to permit or prevent relative rotation of the first and second members. Actuation of the apparatus to prevent relative rotation of the first and second members is achieved by actuating the variable orifice to a closed position so that the flow of fluid from the second chamber back to the first chamber is prevented. The variable orifice is controlled by an electrical control line from a suitable control system. A sensor communicates through the control cable with the surface location in order to communicate unspecified information to the surface location.
U.S. Pat. No. 6,571,888 (Comeau et al) describes an apparatus and a method for directional drilling with coiled tubing. The apparatus includes an uphole sub connected to coiled tubing, a downhole sub having a bent housing, a drill bit and a first motor for rotating the drill bit, a rotary connection between the uphole sub and the downhole sub for enabling rotation therebetween, and a clutch positioned between the rotary connection and the uphole sub. The clutch is operable between engaged and disengaged positions using fluid cycles applied alternately to engage and disengage the clutch. In the engaged position of the clutch, the downhole sub is rotatable relative to the uphole sub. In the disengaged position of the clutch, the downhole sub is locked against rotation relative to the uphole sub. The apparatus may be further comprised of a speed reducer for dissipating the reactive torque tending to rotate the downhole sub when the clutch is in the engaged position.
U.S. Patent Application Publication No. US 2003/0056963 A1 (Wenzel) describes an apparatus for controlling a downhole drilling motor assembly which includes a tubular housing, a mandrel rotatably mounted within the housing, and an hydraulic damper assembly disposed between the housing and the mandrel. The hydraulic damper assembly limits the rate of rotation of the mandrel within the housing in order to provide a preset resistance to reactive torque. The hydraulic damper assembly includes an annular body which is positioned within an annular chamber between the housing and the mandrel. The annular body is connected with the mandrel with splines so that the annular body rotates with the mandrel and can reciprocate axially relative to the mandrel. A guide track on the exterior surface of the annular body engages with guide members on the housing. The guide track has a zig-zag pattern which causes the annular body to reciprocate axially in the annular chamber as the housing rotates relative to the mandrel. The annular chamber is filled with hydraulic fluid. The annular body is provided with hydraulic valves which provide a restricted flow of the hydraulic fluid through the annular body as the annular body reciprocates within the annular chamber, thereby providing the preset resistance which limits the rate of rotation of the mandrel within the housing. The apparatus may be actuated to permit or prevent rotation of the mandrel within the housing. Actuation of the apparatus to prevent rotation of the mandrel within the housing may be achieved by actuating an annular plug to block the hydraulic valves, by actuating a clutch between the mandrel and the housing to lock the mandrel and housing together, or by actuating an electric valve to block the movement of hydraulic fluid within the annular chamber.